Radiant exposure explained

In radiometry, radiant exposure or fluence is the radiant energy received by a surface per unit area, or equivalently the irradiance of a surface, integrated over time of irradiation, and spectral exposure is the radiant exposure per unit frequency or wavelength, depending on whether the spectrum is taken as a function of frequency or of wavelength. The SI unit of radiant exposure is the joule per square metre, while that of spectral exposure in frequency is the joule per square metre per hertz and that of spectral exposure in wavelength is the joule per square metre per metre —commonly the joule per square metre per nanometre .

Mathematical definitions

Radiant exposure

Radiant exposure of a surface, denoted H_e ("e" for "energetic", to avoid confusion with photometric quantities), is defined as$$H\_\backslash mathrm\; =\; \backslash frac\; =\; \backslash int\_0^T\; E\_\backslash mathrm(t)\backslash ,\; \backslash mathrmt,$$where

• ∂ is the partial derivative symbol;
• Q_e is the radiant energy;
• A is the area;
• T is the duration of irradiation;
• E_e is the irradiance.

Spectral exposure

Spectral exposure in frequency of a surface, denoted H_e,ν, is defined as$$H\_\; =\; \backslash frac,$$where ν is the frequency.

Spectral exposure in wavelength of a surface, denoted H_e,λ, is defined as$$H\_\; =\; \backslash frac,$$where λ is the wavelength.

See also

• Exposure (photography)
• Irradiance
• Radiant energy